For evaluating the performance of an internal combustion engine and the corresponding engine design development, it is desirable to provide dynamic measurements of fuel and engine oil consumption during operation of the internal combustion engine. Currently, the available methods for determining oil consumption are primarily (1) the use of a dipstick, (2) drain-weigh techniques, (3) radiometric techniques and (4) sulfur methods. However, there are serious shortcomings particular to each of these methods. In addition, there are shortcomings common to all of these methods such as their failure to provide real-time analysis of oil consumption and their failure to provide information on related fuel consumption during the engine operation.
With regard to the traditional dipstick and drain-weigh techniques, many hours of engine operation are required before enough oil is consumed to obtain repeatable and predictable measurements using these rather imprecise methods. As an example, if it is assumed that an engine operating at 50 miles per hour will consume oil at the rate of approximately 5000 miles per quart, the oil consumption rate will be about 0.01 quart of oil per hour. Due to the excessive periods of operation required before measurements may be made using these techniques, information on the time resolution of engine operation is prohibited. In addition, these techniques are susceptible to a high degree of inaccuracy, since any losses due to oil seal leaks or retention of the oil on surfaces within the engine will lead to an overestimate of oil consumption, while an underestimate of oil consumption may occur due to fuel dissolution with the oil.
There are also methods for determining oil consumption which rely on the monitoring of sulfur dioxide (SO.sub.2), either photometrically or coulometrically, generated from the sulfur in the engine oil during engine operation. This method requires sulfur-free isooctane fuel, which therefore undesirably limits the adaptability of this method. In addition, extensive equipment and manpower are required to maintain the test system. Lastly, this method is also subject to interferences from other major or minor exhaust gas components.
The radiometric method is also known and employed by the art and provides a very precise method for measuring oil consumption. This method involves adding the radioactive bromine tracer 1,2-dibromooctadecane to the oil. The resultant combustion product from the internal combustion engine is trapped within a sodium hydroxide solution and counted by scintillation counting. Though extremely accurate, this method is undesirable because of the significant radioactive health and safety considerations and regulatory requirements necessary for its use. In addition, another shortcoming of this method is that it is essentially a batch process which does not readily lend itself to individual measurements, and further requires the preparation of a fresh bromine tracer for each batch operation because of the short half life of the radioactive bromine tracer.
As a solution to the above, U.S. Pat. No. 4,990,780 to Lee et al., which is assigned to the assignee of this invention, provides a novel method for determining oil consumption which is relatively simple and precise, enables real-time measurements, and additionally provides concurrent dynamic fuel consumption data. Lee et al. utilize nonradioactive tracer compounds, such as bromine or chlorine in the form of organic bromo- or chloro-compounds, which are added to the engine oil in small amounts. Upon complete combustion, the bromine or chlorine is converted into hydrogen bromide (HBr) or hydrogen chloride (HCl), respectively. A sample of the exhaust gases generated by the internal combustion engine and comprising the hydrogen bromide or hydrogen chloride is then collected within a sample cell, where the gas sample is maintained at a pressure at which a distinction between an absorption line of the tracer specie and the absorption lines of a related isotopic species can be discerned. Monochromatic radiation is then transmitted through the gas sample at the frequency of an absorption line for the tracer specie. Tunable diode laser spectroscopy is preferably used to measure the amount of tracer isotope within the resultant HBr or HCl gases in the exhaust gases. Lee et al. teach that this same technique may also be used to determine the corresponding fuel consumption from the CO.sub.2 in the exhaust gases.
In use, several shortcomings have generally been identified regarding the system taught by Lee et al. When using a bromine compound, for example, it was determined that a filter required to protect the sample cell from contaminants within the exhaust gas tended to block and retain the hydrogen bromide, thereby possibly preventing the detection of a signal for hydrogen bromide in the exhaust gas. A major problem identified was that the hydrogen bromide was being lost through dissolution in water that had condensed in the sample line upstream of the sample cell, resulting in a total loss of the tracer signal. Such a problem is exacerbated by the desire to minimize the amount of tracer element present in the oil and also the high amount of water vapor present in the exhaust gas of an internal combustion engine.
Therefore, it would be desirable if improvements in the teachings of Lee et al. could be achieved by which the sample cell could be protected from contaminants, and water condensation could be substantially eliminated upstream of the sample cell, so as to provide a method by which minute amounts of gaseous hydrogen bromide or hydrogen chloride would be present and detectable, even in the presence of a large amount of exhaust water vapor.